Field
One or more embodiments of the present disclosure relate to a binder composition for a secondary battery, and a cathode and a lithium battery including the binder composition.
Description of the Related Technology
Lithium batteries are used in various applications due to their high voltage and high energy density. For example, electric vehicles (HEV or PHEV) need to operate at high temperature, to be charged or discharged with a great amount of electricity, and to be used for a long period of time. Accordingly, electric vehicles require lithium secondary batteries with excellent energy density and lifespan characteristics.
To provide lithium batteries with high energy density and excellent lifespan characteristics, an increase in amounts of an electrode active material and a conductive agent and a decrease in an amount of a binder, in an electrode, are required. However, when the amount of the binder decreases, dispersibility and binding force of at least one of the electrode active material and the conductive agent and flexibility of the electrode active material layer deteriorate. Accordingly, during charging and discharging, the electrode active material may be separated from a current collector and thus, cyclic characteristics may deteriorate. Accordingly, a binder that, even in a small amount, provides dispersibility of electrode active material and/or conductive agent, binding force of an electrode plate, and flexibility of an electrode plate, to an electrode, is required.
For example, a fluoropolymer binder, such as a polar functional group-free polyvinylidene fluoride, swells less with respect to an organic electrolytic solution, and thus, when a battery operates, the binder may contribute to maintaining the structure of an electrode and an active material may have improved dispersibility. However, such a fluoropolymer binder shows poor properties in terms of dispersibility of a conductive agent, binding force of an electrode plate, and flexibility of an electrode plate.
A non fluoropolymer binder, such as an acrylronitrile-acrylic acid-alkylacrylate binder may have, compared to a fluoropolymer binder, improved dispersibility of a conductive agent, improved flexibility of an electrode plate, and improved binding force of an electrode plate. However, the non fluoropolymer binder swells too much with respect to an electrolytic solution. Accordingly, the non fluoropolymer binder is needed to be used only in a restricted amount.
Thus, a binder is required that has improved binding force and flexibility at the same time to improve energy density and lifespan characteristics of a lithium battery.